Expanded polymer pellets

ABSTRACT

The invention refers to a method for producing expanded polymer pellets, which comprises the following steps: melting a polymer comprising a polyamide; adding at least one blowing agent; expanding the melt through at least one die for producing an expanded polymer; and pelletizing the expanded polymer. The invention further concerns polymer pellets produced with the method as well as their use, e.g. for the production of cushioning elements for sports apparel, such as for producing soles or parts of soles of sports shoes. A further aspect of the invention concerns a method for the manufacture of molded components, comprising loading pellets of an expanded polymer material into a mold, and connecting the pellets by providing heat energy, wherein the expanded polymer material of the pellets or beads comprises a chain extender. The molded components may be used in broad ranges of application.

TECHNICAL FIELD

The present invention relates to a method for producing expanded polymerpellets, the polymer pellets obtained therewith as well as their use,such as for producing cushioning elements, for example for sportsapparel or sports shoes. The present invention further relates to amethod for the manufacture of molded components using expanded polymerpellets, articles obtained therewith and the use of the articles, suchas for sound insulation.

PRIOR ART

Expanded polymers or polymer foams are well known from the prior art.From WO 2006/077395 A1, closed-cell polyamide foams are known, which areproduced in the form of sheets and can be further processed to form e.g.seals.

WO 2006/045513 A1 and EP 1650 255 A1 describe the production of across-linked foam of a copolymer having polyamide blocks and polyetherblocks and the use of the foam. WO 2007/082838 A1 relates to expandable,blowing agent-containing thermoplastic polyurethane having a specifichardness. In a similar manner, WO 2010/010010 A1 relates to anexpandable, blowing agent-containing thermoplastic polymer blendcomprising thermoplastic polyurethane and styrene polymer. DE 10 2011108 744 A1 is directed towards a method for the production of shoesoles, wherein plastic bodies made from foamed thermoplastic elastomeron the basis of urethane (TPU) or on the basis of polyetherblockamide(PEBA) are used.

Compared to this, the objective of the present invention is to provideexpanded polymer pellets that can be produced in as wide a processingwindow as possible and that can be further processed to form stableparts which can be used in a broad area of application, e.g. for theproduction of parts having damping properties and a low weight. Afurther objective is to provide an improved method for the manufactureof molded components or articles from expanded polymer pellets.

SUMMARY OF THE INVENTION

According to a first aspect, this objective is solved by a method forproducing expanded polymer pellets, which comprises the following steps:

a. melting a polymer comprising a polyamide;

b. adding at least one blowing agent;

c. expanding the melt through at least one die for producing an expandedpolymer; and

d. pelletizing the expanded polymer.

The invention further concerns polymer pellets produced with the methodas well as their use, e.g. for the production of cushioning elements forsports apparel, in particular for producing soles or parts of soles ofsports shoes. In addition, the invention concerns a shoe, in particulara sports shoe, with such a sole.

The polyamide may, for example, comprise as a basis a polyamide, acopolyamide and/or a polyetherblockamide. Furthermore, thepolyetherblockamide may comprise at least one of the following features:

-   -   a Shore D hardness in the range from 20 to 70 Shore D;    -   a tensile modulus in the range from 10 to 1100 MPa;    -   a content of polyether blocks from 1 to 90% by weight,        preferably from 1 to 75% by weight, more preferably from 1 to        50% by weight, and a content of polyamide blocks from 10 to 99%        by weight, preferably from 25 to 99% by weight, more preferably        from 50 to 99% by weight, in each case based on 100% by weight        of the polyetherblockamide;    -   a density in the range from 1000 to 1030 g/m³; and    -   a melting point/melting range from 110 to 200° C.

The blowing agent may be selected from nitrogen, carbon dioxide,ethanol, isopropanol, or mixtures thereof. Furthermore, a nucleatingagent, a chain extender, or both may be added in step b.

It is possible that the die is a round die. The pressure at the die maylie in the range of 70 to 250 bar. The mass temperature at the die maylie in the range from 150° C. to 170° C.

It is possible that the expanded polymer is pelletized in an underwaterpelletizing device.

A further aspect of the invention concerns expanded polymer pellets,which are obtainable by a method described above. The pellets maycomprise a size in the range from 2 to 10 mm when measured according toISO 9276. Moreover, the pellets may comprise a particle density in therange from 20 to 400 kg/m³. Furthermore, the pellets may comprise a meancell diameter in the range from 10 to 350 m.

A further aspect of the invention concerns the use of the expandedpolymer pellets for producing cushioning elements for sports apparel, inparticular for producing soles for shoes.

A further aspect of the invention concerns a cushioning element forsports apparel, in particular a sole for a shoe or a part thereof,produced using the expanded polymer pellets described above.

A further aspect of the invention concerns a shoe, in particular asports shoe, with a sole as described above.

A further aspect of the invention concerns expanded polymer pelletswhich are based on polyamide, and exhibit a variation of less than 50%in their storage modulus in the temperature range of −40° C. to +40° C.

A second aspect of the invention relates to a method for the manufactureof molded components, comprising

a. loading pellets of an expanded polymer material into a mold; and

b. connecting the pellets by providing heat energy, wherein

c. the expanded polymer material of the pellets comprises a chainextender.

In an exemplary embodiment the chain extender has been provided after apolymerization of the polymer material.

In another exemplary embodiment, the expanded polymer material comprisesa semi-crystalline polymer.

In step b, the heat energy can be provided by means of at least one ofthe following: pressurized steam, electromagnetic radiation, radiofrequency radiation, microwave radiation, infrared radiation,ultraviolet radiation, electromagnetic induction.

In one embodiment, during step b. the pellets are heated to atemperature between a glass transition temperature and below the onsetof melting of the expanded polymer material. In exemplary embodiments,the pellets are heated up to a range of from 100° C. to 5° C. below themelting point of the expanded polymer material. They may be heated up toa range of from 60° C. to 5° C. below the melting point of the expandedpolymer material, such as 40° C. to 5° C. below the melting point of theexpanded polymer material.

The chain extender can comprise at least one selected from a polymericmaterial containing epoxy groups, pyromellitic dianhydride, and styrenemaleic anhydride, or combinations of one or more thereof. In oneembodiment, the chain extender is a styrene-acrylate copolymercontaining reactive epoxy groups, such as a compound of the followingformula:

wherein R₁ to R₅ are H, CH₃, a higher alkyl group, or combinations ofthem; R₆ is an alkyl group, and x, y, and z are each between 1 and 20.

In another embodiment, the chain extender is selected from one or moreof a tri-epoxide or tetra-epoxide. The chain extender may be, forexample, triglycidyl isocyanurate and/or tetraglycidyl diamino diphenylmethane. In another embodiment, the chain extender is selected from oneor more of styrene maleic anhydride. In a further embodiment, the chainextender is pyromellitic dianhydride.

In one embodiment, the polymer is selected from at least one ofpolyamides, polyester, polyetherketones, and polyolefins. The polyamidecan be at least one of homopolyamide, copolyamide, polyetherblockamide,and polyphthalamide. The polyester can be at least one of polybutyleneterephthalate (PBT), thermoplastic polyester ether elastomer (TPEE), andpolyethylene terephthalate (PET). The polyetherketone can be at leastone of polyether ketone (PEK), polyether ether ketone (PEEK), andpolyetherketoneketone (PEKK). The polyolefin can be at least one ofpolypropylene (PP), polyethylene (PE), olefin co-block polymer (OBC),polyolefine elastomer (POE), polyethylene co-vinyl acetate (EVA),polybutene (PB), and polyisobutylene (PIB).

In another embodiment, the polymer is selected from at least one ofpolyoxymethylene (POM), polyvinylidene chloride (PVCD), polyvinylalcohol(PVAL), polylactide (PLA), polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), tetrafluoroethylene (FEP),ethylene-tetrafluoroethylene (ETFE), polyvinylfluoride (PVF),perfluoroalkoxy (PFA), and thermoplastic polyurethanes (TPU).

In an exemplary embodiment, the polymer comprises polybutyleneterephthalate (PBT) and the chain extender comprises at least oneselected from a polymeric material containing epoxy groups, pyromelliticdianhydride, styrene maleic anhydride, or combinations of one or morethereof, in particular a styrene-acrylate copolymer containing reactiveepoxy groups. In another exemplary embodiment, the polymer comprisespolyamide (PA) or polyetherblockamide (PEBA) and the chain extendercomprises at least one selected from a polymeric material containingepoxy groups, pyromellitic dianhydride, styrene maleic anhydride, orcombinations of one or more thereof, in particular a styrene-acrylatecopolymer containing reactive epoxy groups. In a further exemplaryembodiment, the polymer comprises thermoplastic polyester etherelastomer (TPEE) and the chain extender comprises at least one selectedfrom a polymeric material containing epoxy groups, pyromelliticdianhydride, styrene maleic anhydride, or combinations of one or morethereof, in particular a styrene-acrylate copolymer containing reactiveepoxy groups.

A further aspect of the invention relates to a method for themanufacture of molded components, comprising

-   -   a. loading pellets of an expanded polymer material into a mold,        wherein the expanded polymer material of the pellets comprises        an additive increasing the amorphous content of the polymer        material; and    -   b. connecting the pellets by heating the pellets to a        temperature between a glass transition temperature and below the        onset of melting of the expanded polymer material.

In one embodiment of the manufacture method of the second or furtheraspect, the pellets are produced by a method comprising the steps of:

-   -   a. melting a polymer material wherein the melt comprises at        least one polymer, at least one blowing agent and at least one        selected from a chain extender or an additive increasing the        amorphous content of the polymer material;    -   b. expanding the melt through at least one die for producing an        expanded polymer material; and    -   c. pelletizing the expanded polymer material, in particular in        an underwater pelletizer.

In some embodiments, the pellets are produced by the method according tothe first aspect of the invention.

The chain extender may be added in an amount to provide amorphousregions in the expanded polymer material allowing interdiffusion ofpolymer chains across the interfaces of the pellet boundaries, inparticular in an amount of 0.1 to 20% by weight, more particular 1% to10% by weight, such as 1% to 5% by weight, based on 100% by weight ofthe base polymer material.

The base polymer material may be a polyamide, for instance at least oneof homopolyamide, copolyamide, polyetherblockamide, and polyphthalamide,as an example, polyamide 12.

The chain extender may be a polymeric material containing epoxy groups,such as a styrene-acrylate copolymer containing reactive epoxy groups.

It is possible that the pellets of the expanded material have internallyan at least partially ruptured foam structure.

A further aspect of the invention concerns an article, which isobtainable by the method described above with respect to the second orfurther aspect of the invention.

In an exemplary embodiment, the article is produced using pellets of theexpanded material that may have internally an at least partiallyruptured foam structure. Such an article may be used for e.g. soundinsulation.

Another aspect concerns an article as described above, wherein thearticle is provided as at least one of the following: a packagingmaterial, a reusable packaging material, a pallet, an article formedical transportation, an article for chemical transportation, anarticle for breakable goods transportation, an article for interiorinsulation, an article for exterior insulation, an article for pipeinsulation, a geofoam, a temporary housing, a road crash protection, anarticle for appliance insulation, an article for industrial applianceinsulation, a sun visor, a dash board, a car seat, a center console, acar door, a child/baby seat, an article for battery cover/insulation, anarticle for engine insulation, a bumper, a crash structure, a protectivehelmet, an article of protective clothing, a boat fender, a medicalstretcher, a surf/rescue board, a buoy, a boat hull, a snowmobile seat,a core for skis/snowboards/water skis/wakeboards, a jet ski seat, anartificial turf, a venue or playground flooring, a sports hallprotective flooring/wall, a conditioning roller, a resistance weight foraerobics, a swimming aid, an article of furniture, a bean bag, a cowmat, a drone, an article of luggage, a plane seat, a plane/glider wing,an article for aeroplane cabin insulation, a plane food tray, an articlefor airline food trolley insulation, an under floor, an article forheating protection, an article of advanced protective equipment, amedical cast, a turbine/rotor blade core, a run-flat tyre, hand grips,beverage insulation, lamp covers, mattresses.

Another aspect concerns the use of an article produced with the methodaccording to the second or further aspect of the invention, in theproduction of cushioning elements for sports apparel, in particular forthe production of soles for shoes, preferably midsoles.

Another aspect concerns the use of an article produced with the methodaccording to the second or further aspect of the invention, forpackaging applications, reusable packaging, pallets, medicaltransportation, chemical transportation, breakable goods transportation,interior insulation, exterior insulation, pipe insulation, geofoam,temporary housing, road crash protection, appliance insulation,industrial appliance insulation, sun visor, dash board, car seat, centerconsole, car door, child/baby seat, battery cover/insulation, engineinsulation, bumper, crash structures, protective helmet, protectiveclothing, boat fenders, medical stretchers, surf/rescue boards, buoys,boat hulls, snowmobile seats, core for skis/snowboards/waterskis/wakeboards, jet ski seat, artificial turf, venue or playgroundflooring, sports hall protective flooring/walls, conditioning roller,resistance weights for aerobics, swimming aids, furniture, bean bags,cow mats, drones, luggage, plane seats, plane/glider wings, aeroplanecabin insulation, plane food tray, airline food trolley insulations,under floor, heating protection, advanced protective equipment, medicalcast, turbine/rotor blade core, a run-flat tyre, hand grips, beverageinsulation, lamp covers, mattresses.

A further aspect of the invention concerns a shoe, comprising anelement, in particular a sole, obtainable by a method described abovewith respect to the second or further aspect of the invention. Anotheraspect of the invention concerns a shoe comprising a foam element moldedby using a method described above with respect to the second or furtheraspect of the invention.

Preferred embodiments of the invention are described in the followingdescription, the figures and the claims.

BRIEF DESCRIPTION OF THE FIGURES

The figures show:

FIG. 1: an experimental setup for performing steps a. to c. of themethod according to the invention;

FIG. 2: schematic diagram of an underwater pelletizing device forperforming step d. of the method according to the invention;

FIG. 3: schematic diagram of a die face plate of an underwaterpelletizing device;

FIG. 4: a diagram representing storage modulus versus temperature for anexpanded polyamide pellet as produced in Example 1 (ePA12) and acomparative expanded polypropylene (ePP);

FIG. 5a : a diagram representing a hysteresis loop for a test plate madefrom expanded polyetherblockamide pellets as produced in Example 2,wherein the area under the compression branch of the hysteresis loop ishatched;

FIG. 5b : the diagram of FIG. 5a , wherein the area within thehysteresis loop is hatched;

FIG. 5c : a diagram representing the hysteresis loop for the test platemade from the expanded polyetherblockamide pellets produced in Example 2(ePEBA) in comparison with a test plate made of expanded polypropylene(ePP);

FIG. 6: a scanning electron microscopy (SEM) image of an expandedpolyamide pellet as produced in Example 1; and

FIG. 7: a scanning electron microscopy (SEM) image of an expandedpolyetherblockamide pellet as produced in Example 2.

FIG. 8a : a mold when being filled with pellets of an expanded polymermaterial.

FIG. 8b : the mold of FIG. 8b when filled with pellets of an expandedpolymer material.

FIG. 8c : the mold of FIG. 8c when heat energy is applied to thepellets.

FIG. 9: a diagram representing heat flow versus temperature for expandedpolyetherblockamide pellets with different amounts of chain extender(CE).

FIG. 10: a midsole produced by fusing expanded polyetherblockamidepellets with chain extender (CE).

FIG. 11: a diagram representing heat flow versus temperature forexpanded polyetherblockamide pellets with different amounts of chainextender (CE).

FIG. 12: a midsole produced by fusing expanded polyetherblockamidepellets with chain extender (CE).

FIG. 13: a diagram representing heat flow versus temperature forexpanded polybutylene terephthalate (PBT) pellets with different amountsof chain extender (CE).

FIG. 14: a diagram representing heat flow versus temperature forexpanded thermoplastic polyester ether elastomer (TPEE) pellets with andwithout chain extender (CE).

FIG. 15: a diagram representing normalized melting energy versus contentof chain extender (CE) for expanded thermoplastic polyester etherelastomer (TPEE) pellets with and without chain extender (CE).

FIG. 16: a scanning electron microscopy (SEM) image of expandedpolyamide (PA12) pellets/beads.

FIG. 17: a scanning electron microscopy (SEM) image of expandedpolyamide (PA12) pellets/beads comprising chain extender (CE).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following detailed description, preferred examples andembodiments of the invention are described.

First Aspect of the Invention

The polymer used for the production of the expanded polymer pelletscomprises at least one polyamide. The polymer can be on the basis of apolyamide. In particular, the polymer can comprise at least 10% byweight, in particular at least 30% by weight, preferably at least 50% byweight, of a polyamide, in each case based on 100% by weight of thepolymer. Preferred ranges are 10 to 99% by weight, preferably 25 to 99%by weight, more preferably 50 to 99% by weight, of polyamide, in eachcase based on 100% by weight of the polymer. It is also possible thatthe polymer comprises or consists of 100% by weight of polyamide.

The polymer can be on the basis of a polyamide. In particular, thepolymer can comprise at least 10% by weight, in particular at least 30%by weight, preferably at least 50% by weight, of a polyamide, in eachcase based on 100% by weight of the polymer. Preferred ranges are 10 to99% by weight, preferably 25 to 99% by weight, more preferably 50 to 99%by weight, of polyamide, in each case based on 100% by weight of thepolymer. It is also possible that the polymer comprises or consists of100% by weight of polyamide.

Suitable polymers are polyamides or polyamide-containing polymers thatare expandable. Particularly suitable are those having a tensile modulusabove 10 MPa and/or having a low temperature dependency. Suitable are,for example, polyamide-6 (PA 6), polyamide-6.6 (PA 6.6), polyamide-6.10(PA 6.10), polyamide-11 (PA 11), polyamide-12 (PA 12), polyamide-10.12,or polyamide-10.10. Also combinations thereof can be used. Particularlywell suited is PA 11 or PA 12, or a mixture thereof. Preferably, PA 12is used. Suitable polyamides or polyamide-containing polymers arecommercially available.

Particularly well suited is polyetherblockamide (PEBA).Polyetherblockamide is a blockcopolymer with polyamide-segments andpolyether-segments. For example, suitable polyetherblockamides comprisea content of polyether-blocks from 1 to 90% by weight, in particularfrom 1 to 50% by weight, and a content of polyamide-blocks from 10 to99% by weight, in particular from 50 to 99% by weight, in each casebased on 100% by weight of the polyetherblockamide. It is also possibleto use blends or mixtures of two or more, in particular two, differentpolyetherblockamides. It is further possible that the polymer comprisesor consists of 100% by weight of polyetherblockamides. It is furtherpossible that the polymer comprises or consists of 100% by weight ofpolyamide and polyetherblockamides.

Particularly well suited are furthermore polyetherblockamides whichcomprise at least one of the following properties:

-   -   a Shore D hardness in the range from 20 to 70 Shore D, in        particular from 35 to 70 Shore D;    -   a tensile modulus in the range from 10 to 1100 MPa, in        particular from 80 to 1000 MPa;    -   a density in the range from 1000 to 1030 g/m³;    -   a melting point/melting range in the range from 110 to 200° C.,        in particular from 130 to 175° C.

Herein, the Shore D hardness is measured according to ISO 868. Thetensile modulus is measured according to ISO 527-1. The density ismeasured according to ISO 1183. In the present invention, the meltingpoint or melting range, respectively, relates to a measurement accordingto ISO 11357. Herein, the melting point or melting range, respectively,of the polymer designates the point or range at or within which thecrystalline regions of a semi crystalline polymer melt.

Suitable polyetherblockamides are commercially available. They may beproduced by known methods, e.g. by means of copolycondensation ofpolyamide-blocks containing reactive ends with polyether-blockscontaining reactive ends such as described in WO 2006/045513 A1.

From among the mentioned polyamides and polyetherblockamides, mixturesor blends thereof might be used as well. The polymer for producing theexpanded polymer pellets may contain or be blended with another polymerin addition to the polyamide, for example, thermoplastic polyurethane(TPU), polyphenylene ether (PPE), styrene-acrylonitrile (SAN), and/orrubber, in particular TPU. The content of the other polymer may be below50% by weight, in particular below 10% by weight, preferably below 5% byweight, based on 100% by weight of the polymer. In one embodiment, thepolymer used for producing the expanded pellets comprises no (i.e. 0%)thermoplastic polyurethane. In one embodiment the polymer used forproducing the expanded pellets comprises no (i.e. 0%) other polymer thanthe polyamide.

The polymer used for producing the expanded pellets may be used in anyform, for example as granulate or powder, in particular as granulate.Suitable forms of the polymers are commercially available. In case thatthe base or starting polymer contains adherent humidity or water, thepolymer is preferably dried before melting and drying is completed priorto foaming, in accordance with procedures known to the skilled person.

In the first step of the method according to the invention, the polymeris melted. Suitable methods for melting or fusing are known to theperson skilled in the art. The melting may, for example, be done in anextruder. Suitable extrusion devices or extruders are not subject to anyrestrictions. Common extruders or commercially available extruders canbe used, for example single screw or twin screw extruders. The extruderalso serves to homogeneously disperse the polymer.

The dimensioning of the extruders (e.g. design, length and number ofrevolutions of the extruder screws, temperature profile, pressure) maybe chosen by the skilled person, such that added materials arehomogeneously dispersed and intermixed into the melted polymer. Theextruder is usually operated at a temperature at which the polymermaterial is completely melted. Suitable temperatures depend on thepolymer used and can be routinely determined by the skilled person, forexample, for polyamide 12 suitable temperatures are in the range from180 to 320° C., in particular from 220 to 290° C.

It is also possible to use two extruders arranged in series. Goodresults are, for example, obtained, if the first extruder is a twinscrew extruder and the second extruder is a single screw extruder. Thefirst extruder is used to plasticize the material and homogeneouslydisperse additional materials, e.g. a blowing agent. Due to theinclusion of the blowing agent, the viscosity of the material issignificantly reduced, and the second extruder could be used to cooldown the material in order to improve the melt properties and increasethe pressure needed for foaming expansion. This can also be achieved byemploying a single extruder being sufficiently long to allow thematerial to be heated and then cooled in a controlled way. Additionally,it is possible to insert a static mixer between the first and secondextruder. Suitable temperatures for the first extruder lie in the rangefrom 170 to 320° C., in particular in the range from 170 to 220° C. orfrom 220 to 290° C. Suitable temperatures for the second extruder dependstronger on the used polymer, e.g. for polyamide 12 a mass temperaturein the range from 150 to 190° C., in particular from 165 to 180° C., issuitable, and for polyetherblockamide a mass temperature in the rangefrom 130 to 180° C., in particular from 155 to 165° C., is suitable.

An exemplary arrangement 1 is shown in FIG. 1, with a twin screwextruder 2 and a single screw extruder 9. According to FIG. 1, polymeris introduced at hopper 4 and blowing agent 5 is fed by means of aninjection device 6. It is possible to introduce additional materials,e.g. a chain extender, at hopper 4 together with the polymer and/or atthe point of injection device 6 or in the vicinity thereof. The extruder2 is moved via a gear 3. In the extruder 2, the polymer is melted andmixed with the injected blowing agent 5 and optionally additionalmaterial added. According to FIG. 1, an adapter 7 is provided betweenthe extruder 2 and the extruder 9, and the extruder 9 is moved via agear 8. The extruder 9 may, for example, be a cooling extruder. In theextruder 9, the polymer melt is further mixed with the blowing agent andcooled and subsequently extruded through a die 11, preferably a rounddie, such that a foamed or expanded extrudate 12 is obtained. The die 11is connected to the extruder 9 via an adapter 10.

In one embodiment, at least one blowing agent is added to the meltedpolymer. In general, volatile liquids, gases, and decomposable compoundsthat are inert with respect to the polymer melt under the conditionspresent in the extruder and which form a gas, are suitable as a blowingagent. Suitable blowing agents are nitrogen, carbon dioxide, ethanol,isopropanol, or mixtures thereof. Particularly well suited issupercritical carbon dioxide, or a mixture of supercritical carbondioxide with ethanol. The blowing agent may be fed to the extruder withthe base polymer with or without being previously mixed. Alternatively,the blowing agent may be added to the polymer melt at a suitablelocation of the extruder and be intermixed within the extruder.Suitably, the blowing agent is homogeneously dispersed in the polymer ormelted polymer. The amount of added blowing agent lies in the range from1 to 20% by weight, in particular from 1 to 10% by weight, in each casebased on 100% by weight of the polymer melt. Particular amounts ofblowing agent are 1, 2, 3, 4, 5, 7.5, 10 or 15% by weight, based on 100%by weight of the polymer melt. Particularly suitable is e.g. a carbondioxide-ethanol mixture with 2 to 6% by weight of carbon dioxide and 2to 4% by weight of ethanol, based on 100% by weight of the polymer melt.

In addition to the blowing agent, further conventional additives ormaterials that facilitate the processing may be added to the polymermelt in the extruder, for example, a nucleating agent, a chain extender,flame inhibitors, plasticizers, reinforcing agents, pigments, dyes,heat- or light-stabilizers, antistatic agents, fillers, or mixturesthereof. Suitable nucleating agents are additives which can be bothsoluble and not soluble in the polymer melt to promote foam cellnucleation. Examples of non-soluble nucleating agents include talc, orsilica. It is also possible to add a crosslinking agent to the polymermelt. Crosslinking agents are described e.g. in WO 2006/045513 A1 and EP1 650 255 A1. In one embodiment, no crosslinking agent is used, or thepolymer pellets are not crosslinked.

In one embodiment, at least one chain extender is added to the polymermelt. It is also possible to feed at least one chain extender togetherwith the polymer to the extrusion device. Suitable chain extenders arecompounds which increase the melt strength of the polymer melt.Particularly suitable chain extenders are oligomeric or polymericcompounds with reactive groups, e.g. epoxy groups, which react with themelted polymer to increase the molecular weight and degree of branching,thus improving the rheological properties, such as the melt viscosityand the melt strength of the polymer used. Suitable chain extenders canbe based on styrene-acrylate copolymers and are commercially available,e.g. Joncryl® ADR-4368C of BASF. Suitable amounts of chain extender are0.05 to 10% by weight, in particular 0.1 to 5% by weight or 0.1 to 3% byweight, based on 100% by weight of the polymer. The use of chainextenders is particularly beneficial when using polyetherblockamides aspolymers for the production of the expanded pellets.

In one embodiment, the polymer for producing the expanded pelletscomprises polyetherblockamide or consists of polyetherblockamide, and achain extender is added as additional material to the polymer melt.

In addition, it is also possible to melt the polymer together withgranulate made of used tires (rubber) and caoutchouc powder. The thermaldecomposition of the compounds in the extruder leads to the formation ofcracked gas (nitrogen and carbon monoxide), which can act as blowingagent, and carbon, which can act as reinforcing and nucleating agent.

After extrusion the melt is expanded through a die. The die may, forexample, be a round die or a slit die, in particular a round die. Thediameter of the die depends on the size of the extruder, the desiredparticle size and density, and may be e.g. in the range from 1 to 5 mm.Expediently, the die is attached to the extruder. The pressure at thedie depends on the polymer material used and density specification, andmay lie in the range from 40 to 400 bar, in particular in the range from60 to 250 bar. Preferably, for polyamide the pressure may lie in therange from 80 bar to 220 bar, and for polyetherblockamide the pressuremay lie in the range from 45 bar to 200 bar. The mass temperature at thedie depends on the polymer melt and may lie in the range from 140 to180° C., in particular from 150 to 170° C.

Inside the die and particularly after leaving the die, the melt issubjected to a sudden pressure drop and the polymer expands or foams.Depending on the shape of the die, the expanded or foamed polymer isobtained as a strand or a foil. Preferably, a round die is used toobtain a strand. The expanded polymer or foam is stabilized by cooling.Cooling can be done in an under-water pelletizing device, a water bath,a conveyor belt, or a calibration unit where the geometry of the foamstrand also can be adjusted.

Subsequently, the expanded polymer is pelletized. Suitable pelletizingdevices are known to the skilled person, e.g. an under-water pelletizingdevice or an under-water granulator. The pelletizing may, for example,be performed in an under-water pelletizing device which enables bothcontrolled cooling of the expanded polymer and pelletizing. Such devicesare commercially available. Their operation is based on the principlethat the polymer strand leaving the die is cut into discrete particlesin a cutting chamber that is completely filled with water. Thedimensions of the cut particles depend upon the cutting speed andthroughput of the extruder/die and also the dimensions of the die.Suitable temperatures for the water in the cutting chamber are in therange of from 20 to 100° C., in particular from 50 to 100° C.,preferably from 70 to 90° C. Due to the temperature difference betweenthe extrudate having been expanded through the die and the water in thecutting chamber, the polymer immediately solidifies in form ofparticles, preferably sphere-like particles. The pelletizing device isexpediently positioned directly after the die. A suitable under-waterpelletizing device is for example shown in FIG. 2. Another suitableunderwater pelletizer is described in U.S. Pat. No. 5,629,028.

FIG. 2 shows an exemplary arrangement for a device 100 for under-waterpelletizing with die face plate 101, cutting blade assembly 102 andwater circulation housing 103. As shown, the expanded polymer 12 (seeFIG. 1) passes, via an extruder die 104, the die face plate 101 and issubsequently cut into particles 105 by the cutter blade assembly 102which is surrounded by water circulating in the housing 103. Theextruder die 104 is arranged between the extruder and the under-waterpelletizing device 100, and conveys the expanded polymer 12 from theextruder to the under-water pelletizing device 100. The particles 105are leaving the water circulation housing 103 and are subsequently dried(not shown). The under-water pelletizing device 100 is driven by gear106.

FIG. 3 shows a schematic diagram of a die face plate 101 of anunderwater pelletizing device. The die face plate 101 contains holes107. The number of holes depends on the dimensions or size of theextrusion device. In exemplary embodiments, the diameter of the holes isbetween 2.3 mm and 2.6 mm and the number of holes between 1 and 4, e.g.there may be 2 holes when using a diameter of 2.3 mm.

The shape and size of the expanded polymer pellets can be adjusted bye.g. the throughput in the extruder, the shape of the die, thetemperature and pressure at the die, the water temperature and waterpressure in an under-water pelletizer, the cutting speed of the bladesof the pelletizer. The selection of suitable conditions lies within theroutine skill and knowledge of the skilled person.

The expanded polymer pellets may have a spherical shape, an ellipsoidshape, or triangular shape. Preferably, the pellets have substantiallyspherical shape. If the pellets are essentially spherical in shape, theymay, for example, comprise a size from 2 to 10 mm when measuredaccording to ISO 9276, and a particle density in the range from 20 to400 kg/m³, e.g. from 50 to 300 kg/m³. Suitable mean cell diameters arewithin the range from 10 to 350 m.

The invention also concerns expanded polymer pellets which are based onpolyamide, and exhibit a variation of less than 40%, preferably avariation in the range of 30 to 40%, in their storage modulus in thetemperature range of −40° C. to +40° C. Preferably, they have a densityin the range of from 70 to 100 kg/m³.

The invention further concerns expanded polymer pellets which are basedon polyetherblockamide, and when formed into a test plate exhibit arelative energy loss during a full hysteresis cycle (after 10 or morecycles) in the range from 10 to 90%, preferably from 10 to 35%.Preferably, they have a density in the range of from 50 to 90 kg/m³.Herein, the relative energy loss during a full hysteresis cycledesignates the quotient of the area (integral) within the hysteresisloop divided by the total energy exerted during compression, i.e. thearea (integral) under the compression branch of the hysteresis loop in aforce versus compressive strain (displacement) diagram. This isillustrated in FIGS. 5b and 5a , respectively, and further described inExample 2 below.

The expanded polymer pellets can be used in a wide range ofapplications. The expanded polymer pellets may be processed to formcomponents that are very light-weight and show good temperatureperformance and temperature independence. They can be processed toproduce components exhibiting light-weight, good elasticity and goodenergy resilience in a wide temperature range.

The expanded polymer pellets are therefore very well suited forproducing cushioning elements or components with cushioning properties,such as for sport apparel, for example for producing soles for shoes, inparticular sports shoes. To this end, the expanded polymer pellets areexpediently loaded into a mold comprising a cavity having a shape thatcorresponds to the component being produced. Therein, the expandedpolymer pellets are connected to each other, in particular by lettingheat act on them, for example by feeding pressurized steam to the mold.

The invention also concerns sports apparel and shoes, in particularsports shoes, produced using of the expanded polymer pellets.

Other applications of use for the expanded polymer pellets are areaswhere cushioning or damping properties and high stability within a largetemperature range are desirable, e.g. in the automotive sector oraviation industry. They also can be used to form components having goodenergy absorbing properties. They are, for example, suitable incomponents for automotive crash protection.

Second Aspect of the Invention

In a second aspect, the invention concerns a method for the manufactureof molded components, comprising loading pellets or beads of an expandedpolymer material into a mold, and connecting the pellets or beads byproviding heat energy, wherein the expanded polymer material of thepellets or beads comprise a chain extender. The terms “pellets” and“beads” are used interchangeably herein.

As an example, the chain extender can be provided after a polymerizationof the polymer material. For example, the chain extender can be added ina separate compounding step and/or immediately before expanding thepolymer material. The chain extender may be incorporated into the basepolymer material that is used for the production of the pellets of theexpanded polymer material. The chain extender may be added to the basepolymer in a compounding stage. Alternatively, the base polymer may befirst supplied to the polymer processing apparatus, e.g. an extruder,via a supply, e.g. a hopper, and then the chain extender may be added.

For connecting the pellets, heat energy may be provided in a variety ofdifferent ways. The heat energy may for example be provided in the formof pressurized steam that is supplied to the molding tool. Alternativelyor in addition, the heat energy may also be provided by means of anelectromagnetic field. The heat energy may for example be provided byirradiating the molding tool and/or the pellets with electromagneticradiation. The electromagnetic radiation may for example be selectedfrom one or more of the following frequency ranges: radio frequencyradiation (30 kHz-300 MHz), microwave radiation (300 MHz-300 GHz),infrared radiation (300 GHz-400 THz), ultraviolet radiation (789 THz-3PHz), or from another frequency range. The heat energy may also beprovided by means of electromagnetic induction. An energy absorbingmaterial may be added to the pellets, to increase the amount of heatenergy absorbed by the pellets, for example when irradiated withelectromagnetic radiation or being heated by electromagnetic induction.All of the above mentioned possibilities may be combined with oneanother.

During step b. the pellets can be heated to a temperature between aglass transition temperature and below the onset of melting of theexpanded polymer material. This heating leads to an increase of theamorphous chain mobility and to bead to bead fusion of the expandedpolymer pellets. As an example, the heating is preferably conductedabove a glass transition temperature of the expanded polymer material.In exemplary embodiments, the pellets are heated up to a range of from100° C. to 5° C. below the melting point of the expanded polymermaterial. They may be heated up to a range of from 60° C. to 5° C. belowthe melting point of the expanded polymer material, such as 50° C. to 5°C. below or 40° C. to 5° C. below the melting point of the expandedpolymer material.

The term “onset of melting” as used herein means the temperature atwhich the polymer material starts to melt. This may be determined e.g.according to DSC (differential scanning calorimetry), such that, in adiagram of heat flow versus temperature, the temperature at which theheat flow increases indicates the onset of melting. The term “meltingpoint” as used herein, means e.g. the melting peak obtained by DSC.Suitable conditions for DSC are e.g. a heating rate of 10 K/min for atemperature range of 25° C. to 250° C. The glass transition temperatureof the expanded polymer material also can be determined by, for example,DSC.

The chain extender can comprise at least one compound selected from apolymeric material containing epoxy groups, pyromellitic dianhydride,and styrene maleic anhydride, or combinations of two or more thereof.Suitable chain extenders are styrene-acrylate copolymers containingreactive epoxy groups, for example, a compound of the following formula:

wherein R₁ to R₅ are H, CH₃, a higher alkyl group, or combinations ofthem; R₆ is an alkyl group, and x, y, and z are each between 1 and 20.Such a chain extender is commercially available as Joncryl® ADR-4368C(of BASF)

The chain extender also may be a tri-epoxide, tetra-epoxide, or acombination thereof. Suitable chain extenders are, for example,triglycidyl isocyanurate and/or tetraglycidyl diamino diphenyl methane.Another suitable chain extender is a styrene maleic anhydride. A furthersuitable chain extender is pyromellitic dianhydride.

The expanded polymer material may comprise a semi-crystalline polymer,or a polymer blend containing at least one semi-crystalline polymer.

The polymer of the expanded polymer material may be polyamide,polyester, polyetherketone, polyolefin, or a combination thereof. Thepolyamide can be homopolyamide, copolyamide, polyetherblockamide,polyphthalamide, or a combination thereof. A very suitable material ispolyetherblockamide (PEBA). Generally the polyamides can be the samepolyamides as defined above in the context of the first aspect of theinvention. The polyester can be polybutylene terephthalate (PBT),thermoplastic polyester ether elastomer, (TPEE), polyethyleneterephthalate (PET), or a combination thereof. The polyetherketone canbe polyether ketone (PEK), polyether ether ketone (PEEK),polyetherketoneketone (PEKK), or a combination thereof. The polyolefincan be polypropylene (PP), polyethylene (PE), olefin co-block polymer(OBC), polyolefine elastomer (POE), polyethylene co-vinyl acetate (EVA),polybutene (PB), polyisobutylene (PIB), or a combination thereof.

Other suitable polymers are polyoxymethylene (POM), polyvinylidenechloride (PVCD), polyvinylalcohol (PVAL), polylactide (PLA),polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),tetrafluoroethylene (FEP), ethylene-tetrafluoroethylene (ETFE),polyvinylfluoride (PVF), perfluoroalkoxy (PFA), thermoplasticpolyurethane (TPU), or a combination thereof.

As an example, the polymer comprises polybutylene terephthalate (PBT)and the chain extender comprises a polymeric material containing epoxygroups. As a further example, the polymer comprises PBT and the chainextender comprises pyromellitic dianhydride. As a further example, thepolymer comprises PBT and the chain extender comprises styrene maleicanhydride. As a further example, the polymer comprises PBT and the chainextender comprises a styrene-acrylate copolymer containing reactiveepoxy groups, or e.g. Joncryl® ADR-4368C.

As another example, the polymer comprises polyamide, such as polyamide12, or polyetherblockamide (PEBA), and the chain extender comprises apolymeric material containing epoxy groups. As a further example, thepolymer comprises polyamide, such as polyamide 12, orpolyetherblockamide (PEBA), and the chain extender comprisespyromellitic dianhydride. As a further example, the polymer comprisespolyamide, such as polyamide 12, or polyetherblockamide (PEBA), and thechain extender comprises styrene maleic anhydride. As a further example,the polymer comprises polyamide, such as polyamide 12, orpolyetherblockamide (PEBA), and the chain extender comprises astyrene-acrylate copolymer containing reactive epoxy groups or e.g.Joncryl® ADR-4368C.

In a further exemplary embodiment, the polymer comprises thermoplasticpolyester ether elastomer (TPEE) and the chain extender comprises apolymeric material containing epoxy groups. As a further example, thepolymer comprises TPEE and the chain extender comprises pyromelliticdianhydride. As a further example, the polymer comprises TPEE and thechain extender comprises styrene maleic anhydride. As a further example,the polymer comprises TPEE and the chain extender comprises astyrene-acrylate copolymer containing reactive epoxy groups or e.g.Joncryl® ADR-4368C.

In a further aspect, the invention concerns a method for the manufactureof molded components, comprising loading pellets of an expanded polymermaterial into a mold, wherein the expanded polymer material of thepellets comprises an additive increasing the amorphous content of thepolymer material; and connecting the pellets by heating the pellets to atemperature between a glass transition temperature and below the onsetof melting of the expanded polymer material. The heating can be carriedout as described above. An additive increasing the amorphous content ofthe polymer material modifies the polymer such that better connecting ofthe pellets in the mold is achieved. Such an additive can be a chainextender, without being restricted thereto.

The pellets used for manufacturing the molded components may be producedby using the above described methods using either a chain extender or anadditive increasing the amorphous content of the polymer material, or acombination thereof. It is also possible to provide for two or moremelting stages before expansion. It is also possible to add the blowingagent and chain extender or additive in two or more melting stagesbefore expanding, e.g. melting the polymer, adding the chain extender oradditive, then cooling, melting the polymer, and adding the blowingagent. Further possible is melting the polymer, adding a chain extender,then cooling, and repeating the process but with adding the blowingagent.

The chain extender may be added in an amount of 0.1 to 20% by weight, inparticular 0.1 to 15% by weight, preferably 0.1 to 10% by weight, suchas 0.1 to 5% by weight or 1 to 5% by weight, based on 100% by weight ofthe base polymer material. The same amounts may be used for an additiveincreasing the amorphous content of the polymer material.

Particularly suitable base polymer material are selected from polyamidesand are, for instance, homopolyamide, copolyamide, polyetherblockamide,and polyphthalamide. Very suitable is, as an example, polyamide 12.

The chain extender may be a polymeric material containing epoxy groups,such as a styrene-acrylate copolymer containing reactive epoxy groups.

FIGS. 8a, 8b and 8c show a mold which can be used to conduct the methodfor the manufacture of molded components according to the second aspectof the invention. FIG. 8a shows a mold, generally designated withreference numeral 200 and comprising two parts 201 and 202. The mold 200comprises a cavity 205 which is filled with pellets 220 via a supplytube 210. FIG. 8b shows when the cavity 205 is completely filled withpellets 220. FIG. 8c shows the application of heat energy 230 on thepellets 220, in order to connect the pellets. After having connected thepellets, the mold 200 can be opened via parts 201 and 202 to release themolded component (not shown).

Molded components can be manufactured in a molding from the pellets ofthe expanded polymer material using steam-chest molding. This technologyas well as steam-chest molding machines are known in the art. Suchsteam-chest molding machines are commercially available, e.g. from thecompany Kurtz GmbH (Germany). In this process, first the pellets are fedinto the mold. After closing the mold, the pellets are subjected tosteam pressure. The conditions used for steam pressure and temperatureare dependent on the material of the pellets used (polymer material,chain extender, additive). These conditions can be determined by theperson skilled in the art using routine experiments. The temperature canbe chosen such as to be, on the one hand, above the glass transitiontemperature of the polymer material to allow additional mobility of theamorphous regions in the polymer and, on the other hand, below the onsetof melting of the polymer material so that the foamed pellets do notbegin to melt and ultimately collapse. As an example, the molding can beconducted using a steaming profile with a ramping thepressure/temperature up and down for a predetermined time of duration.The skilled person can determine suitable pressure, temperature, andtime/cycle conditions by balancing e.g. pressure and time. If thepressure is too high, the pellets can collapse and melt. If the time istoo short, the pellets will not receive enough energy and may not fusecorrectly. It is also possible to use the melting material of thepolymer material to create fusion, for example, for expandedpolypropylene having double melting peak with fusion occurring betweenmelting peaks.

It is possible that the pellets of the expanded material have internallyan at least partially ruptured foam structure.

If the article is produced using pellets of the expanded material thatmay have internally an at least partially ruptured foam structure, themolded component produced is suitable for e.g. sound insulation.

The molded components produced may be used as or be suitable as at leastone of the following: a packaging material, a reusable packagingmaterial, a pallet, an article for medical transportation, an articlefor chemical transportation, an article for breakable goodstransportation, an article for interior insulation, an article forexterior insulation, an article for pipe insulation, a geofoam, atemporary housing, a road crash protection, an article for applianceinsulation, an article for industrial appliance insulation, a sun visor,a dash board, a car seat, a center console, a car door, a child/babyseat, an article for battery cover/insulation, an article for engineinsulation, a bumper, a crash structure, a protective helmet, an articleof protective clothing, a boat fender, a medical stretcher, asurf/rescue board, a buoy, a boat hull, a snowmobile seat, a core forskis/snowboards/water skis/wakeboards, a jet ski seat, an artificialturf, a venue or playground flooring, a sports hall protectiveflooring/wall, a conditioning roller, a resistance weight for aerobics,a swimming aid, an article of furniture, a bean bag, a cow mat, a drone,an article of luggage, a plane seat, a plane/glider wing, an article foraeroplane cabin insulation, a plane food tray, an article for airlinefood trolley insulation, an under floor, an article for heatingprotection, an article of advanced protective equipment, a medical cast,a turbine/rotor blade core, a run-flat tyre, hand grips, beverageinsulation, lamp covers, mattresses.

The molded components produced may be used as or be suitable as anarticle, in the production of cushioning elements for sports apparel, inparticular for the production of soles for shoes, preferably midsoles.

An aspect of the invention concerns a shoe, in particular a shoecomprising a cushioning element. The cushioning element may be a sole,in particular a midsole. Suitable midsoles may be produced e.g. byfusing expanded polyetherblockamide pellets containing chain extender.Such midsoles are shown in FIG. 10 and FIG. 12 and further described inExamples 3 and 4 below.

Another aspect of the invention concerns an article comprising a foam.The foam can be produced by fusing or connecting expanded polymerpellets using the methods described above. The article may be sportapparel, for example a shoe, such as a sports shoe. The shoe maycomprise the foam in form of a cushioning element, e.g. as sole ormidsole.

The molded components also may be used for sound insulation. Suitablemolded components are in particular foams with open cell configuration.As an example, the expanded pellets, and thus the fused foam may have anat least partially ruptured structure. Pellets or fused foams suitablefor producing sound insulation articles may be produced e.g. frompolyamide, such as polyamide 12. The polyamide may contain a chainextender. Such expanded pellets are shown in FIGS. 16 and 17. FIG. 16shows a scanning electron microscopy (SEM) image of expanded polyamide(PA12) pellets without (i.e. 0%) chain extender. FIG. 17 shows ascanning electron microscopy (SEM) image of expanded polyamide (PA12)pellets comprising 1.5% chain extender. The enlargement scale in thosefigures is 200-times of a distance of 100 μm as shown. Those figuresshow that the cells rupture when increasing the percentage of chainextender.

EXAMPLES

The invention is illustrated by means of the following examples thatshow embodiments but do not limit the invention.

Example 1

As base polymer, a polyamide 12 material was used. The polyamide 12 usedwas Vestamid LX 9012 obtainable from Evonik Industries AG, Marl. Asblowing agent, a combination of 4% by weight of (supercritical) carbondioxide and 3% by weight of ethanol, based on 100% by weight of the basepolymer, was used.

The base polymer and blowing agent were fed to the twin screw extruder 2according to the setup shown in FIG. 1, wherein the reference signsdesignate the same as in the discussion of FIG. 1 above. In the extruder2, the polymer introduced via hopper 4 was melted and mixed with theinjected blowing agent 5. The temperature profile in the extruder 2 wasin the range of from 170 to 220° C. In the cooling extruder 9, thepolymer melt was further mixed with the blowing agent and cooled. Themass temperature in the extruder 9 was 170° C. Subsequently, the moltenpolymer was expanded through a round die 11 at a pressure of 220 bar,resulting in an expanded extrudate 12 in strand form. Thereafter, theexpanded extrudate 12 was fed to an underwater pelletizing device asshown in FIG. 2. The temperature in the water circulation system of theunderwater pelletizer was 70° C. The pellets obtained were dried afterunderwater pelletizing, and prior to density measurements. They had adensity of 89 kg/m³.

The pellets were investigated by means of DMA (dynamic mechanicalanalysis) to evaluate the storage modulus at different temperatures, andfurther by scanning electron microscopy (SEM).

For DMA, a known test apparatus was used and a storage modulus analysiswas carried out with a −40° C. to +40° C. temperature sweep under thefollowing test conditions: 5° C. increments; 5 min soak time at eachtemperature; 25% initial compression strain; 5% sinusoidal oscillationaround initial strain; and 1 Hz oscillation. The pellets tested hadsubstantially spherical shape with approximately 5 mm diameter. Theresults obtained are shown in FIG. 4 showing the storage modulus (inkPa) versus the temperature (in ° C.) for EPA12. For comparison,measurements of a foamed polypropylene (Neopolen P9230K of BASF; EPP)having spherical shape with approximately 4-5 mm diameter and similarstiffness properties are further shown in FIG. 4.

As is evident from that figure, the polyamide pellets EPA12 show avariation of approx. 35%, more precisely a decrease by approx. 35% instorage modulus when changing the temperature from −40° C. to +40° C.,compared to the expanded polypropylene particles EPP with approx. 288%decrease in storage modulus.

In FIG. 6, a scanning electron microscopy (SEM) image of the expandedpolyamide pellet is shown. The enlargement scale is 20-times of adistance of 1 mm as shown. The image shows that the pellets have closedparticle skin and uniform cell sizes, thus, providing an excellent foamstructure in particle form.

Example 2

As base polymer, a PEBA material was used. The used PEBA material wasVestamid E62-S3 obtainable from Evonik Industries AG, Marl. According tosupplier's information the number following the letter E indicates theShore D hardness according to ISO 868, meaning that Vestamid E62-S3comprises a Shore D hardness of 62. As blowing agent, a combination of4% by weight of (supercritical) carbon dioxide and 2% by weight ofethanol, based on 100% by weight of the base polymer, was used. Further,a chain extender based on styrene-acrylate copolymer was used. The chainextender was Joncryl® ADR-4368C of BASF which was used in an amount of2% by weight, based on 100% by weight of the base polymer.

The base polymer, blowing agent and chain extender were fed to the twinscrew extruder 2 according to the setup shown in FIG. 1, wherein thereference signs designate the same as in the discussion of FIG. 1 above.In the extruder 2, the polymer introduced via hopper 4 was melted andmixed with the injected blowing agent 5 and the chain extender. Thechain extender was introduced with the polymer as a dry blend in thehopper. The temperature profile in the extruder 2 was in the range offrom 170 to 220° C. In the cooling extruder 9, the polymer melt wasfurther mixed with the blowing agent and chain extender, and cooled. Themass temperature in the extruder 9 was 158° C. Subsequently, the moltenpolymer was expanded through a round die 11 at a pressure of 200 bar,resulting in an expanded extrudate 12 in strand form. Thereafter, theexpanded extrudate 12 was fed to an underwater pelletizing device asshown in FIG. 2. The temperature in the water circulation system of theunderwater pelletizer was 70° C. The pellets obtained were dried afterunderwater pelletizing, and prior to density measurements. They had adensity of 70 kg/m³ and were investigated by scanning electronmicroscopy (SEM).

Further, for evaluating mechanical properties, the pellets were bondedtogether via steam to produce a test plate. The test plate had a densityof approx. 84 kg/m³ and was tested with regard to its compressionbehavior.

The compression testing was carried out using a known testing apparatusat 23° C. under the following test conditions: 20 mm thick sample; 50%compression; heel stamp (diameter of 50 mm); speed of 50 mm/min; and 5Npre-load. The results obtained are shown in FIGS. 5a, 5b and 5c . Forcomparison, measurements of a similar test plate made from foamedpolypropylene (Neopolen P9230K of BASF; EPP) having similar stiffnessproperties are shown in FIG. 5 c.

The diagram in FIG. 5a shows the hysteresis loop for the first cycle forthe test plate made from the expanded polyetherblockamide pellets,wherein the total energy exerted during compression of the test plate ishatched. The diagram of FIG. 5b shows the same diagram as FIG. 5a ,however, with the area within the hysteresis loop being hatched. Formthe hatched areas in FIG. 5b and FIG. 5a , the relative energy loss in %during one full hysteresis cycle can be calculated by dividing the areahatched in FIG. 5b by the area hatched in FIG. 5a . The relative energyloss during the first hysteresis cycle for the test plate made from theexpanded pellets of the present example was approximately 57%. Furthertest cycles were conducted, wherein in the tenth cycle the relativeenergy loss was approximately 31%.

The diagram of FIG. 5c shows the hysteresis loop for the test plate madefrom the expanded polyetherblockamide pellets (ePEBA), in comparisonwith a test plate made from expanded polypropylene pellets (ePP). Thevalues show that the ePEBA test plate demonstrates good mechanicalproperties during compression up to 50% compressive strain(displacement) with good recovery (low plastic deformation) and lowhysteresis, thus improved compression properties when compared with theePP plate.

In FIG. 7, a scanning electron microscopy (SEM) image of the expandedpolyetherblockamide pellet is shown. The enlargement scale is 20-timesof a distance of 1 mm as shown. The image shows that the pellets haveclosed particle skin and uniform cell sizes, thus, providing anexcellent foam structure in particle form.

Example 3

As base polymer, a PEBA material was used. The used PEBA material wasVestamid E62-S3 obtainable from Evonik Industries AG, Marl. Further, achain extender based on styrene-acrylate copolymer, namely Joncryl®ADR-4368C (BASF) was used in amounts of 1% by weight, 2% by weight, and2.5% by weight, based on 100% by weight of the base polymer. Forcomparison, the base polymer was also tested without chain extender. Thepolymer together with the same blowing agents as described in Example 2and the indicated amount of chain extender were melted in an extruder,similar to Example 2. Subsequently, similar to Example 2, the melt wasexpanded through a round die and fed to an underwater pelletizing deviceto obtain expanded pellets.

The pellets (before molding) were tested on their heat flow-temperaturebehavior via DSC measurement using a heating rate of 10K/min for atemperature range of from 25° C. to 250° C. The test results obtainedare shown FIG. 9, wherein the data from the first heating of the DSCmeasurement were used. In FIG. 9, the designations of the curvesindicate the amount of chain extender and, if, the offset of the curvecompared to zero. The curves have an indicated offset of 0.5, 1, and1.5, respectively, for better comparison. As can be seen, neither thepeak nor the width of the curve is affected by the chain extender.However, the height of the peak is affected in that the height isdecreasing with increasing amount of chain extender. That means that thecrystallinity of the polymer decreases with increasing amount of chainextender.

The pellets containing 2.5% by weight of chain extender were loaded intoa mold and fused by providing steam into the mold. The mold was a toolfor molding midsoles for shoes. FIG. 10 shows an image of the midsoleobtained after molding.

Example 4

As base polymer, a PEBA material was used. The used PEBA material wasVestamid E55 obtainable from Evonik Industries AG, Marl. A chainextender based on styrene-acrylate copolymer, namely Joncryl® ADR-4368C(BASF), was used in amounts of 3% by weight, 4.5% by weight, and 5% byweight, based on 100% by weight of the base polymer. For comparison, thebase polymer was also tested without chain extender. The polymertogether with the same blowing agents as described in Example 2 and theindicated amount of chain extender were melted in an extruder, similarto Example 2. Subsequently, similar to Example 2, the melt was expandedthrough a round die and fed to an underwater pelletizing device toobtain expanded pellets.

The pellets (before molding) were tested on their heat flow-temperaturebehavior via DSC measurement using a heating rate of 10 K/min for atemperature range of from 25° C. to 250° C. The test results obtainedare shown FIG. 11, wherein the data from the first heating of the DSCmeasurement were used. In FIG. 11, the designations of the curvesindicate the amount of chain extender and, if, the offset of the curvecompared to zero. The curves have an indicated offset of 0.5, 1, and1.2, respectively, for better comparison. As can be seen, the height ofthe peak is affected in that the height is decreasing with increasingamount of chain extender. That means that the crystallinity of thepolymer decreases with increasing amount of chain extender.

The pellets containing 5% by weight of chain extender were loaded into amold and fused by providing steam into the mold. The mold was a tool formolding midsoles for shoes. FIG. 12 shows an image of the midsoleobtained after molding.

Example 5

As base polymer, a polybutylene terephthalate (PBT) material was used.The used PBT material was Ultradur B4520 obtainable from BASF. A chainextender based on styrene-acrylate copolymer, namely Joncryl® ADR-4368C(BASF), was used in amounts of 1% by weight and 1.5% by weight, based on100% by weight of the base polymer. For comparison, the base polymer wasalso tested without chain extender. A compact material was formed,wherein the process included melting of the polymer, adding the chainextender and extrusion of the resulting material. Subsequently, thecompact material was cooled and the material's heat flow-temperaturebehavior was measured using DSC using a heating rate of 10 K/min for atemperature range of from 25° C. to 250° C. The test results obtainedare shown FIG. 13, wherein the data from the first heating of the DSCmeasurement were used. In FIG. 13, the designations of the curvesindicate the amount of chain extender and, if, the offset of the curvecompared to zero. The curves have an indicated offset of 1 and 2,respectively, for better comparison. As can be seen, the peak of thecurve is affected by the chain extender in its height. The height of thepeak is decreasing with increasing amount of chain extender. That meansthat the crystallinity of the polymer decreases with increasing amountof chain extender.

Example 6

As base polymer, a TPEE material was used. The used TPEE material wasArnitel EM400 obtainable from DSM. A chain extender based onstyrene-acrylate copolymer, namely Joncryl® ADR-4368C (BASF), was usedin an amount of 2% by weight, based on 100% by weight of the basepolymer. For comparison, the base polymer was also tested without chainextender. A compact material was formed, wherein the process includedmelting of the polymer, adding the chain extender and extrusion of theresulting material. Subsequently, the compact material was cooled andthe material's heat flow-temperature behavior was measured using DSCusing a heating rate of 10 K/min for a temperature range of from 25° C.to 250° C. The test results obtained are shown in FIG. 14 and FIG. 15,wherein the data from the first heating of the DSC measurement wereused. In FIG. 14, the designations of the curves indicate the amount ofchain extender and, if, the offset of the curve compared to zero. Onecurve has an indicated offset of 0.2, for better comparison. As can beseen, the peak of the curve is affected by the chain extender in itsheight. The height of the peak is decreasing with the presence of chainextender. That means that the crystallinity of the polymer decreaseswith addition of a chain extender. Further, the curve is smoother whenchain extender has been added.

FIG. 15 shows that the melting energy (normalized) significantlydecreases by 29% when adding chain extender in an amount of 2% byweight. This illustrates the change in crystallinity due to chainextender addition. The same tendency would be seen when plotting theresults of expanded PEBA of Example 4 above (FIG. 11) and of expandedPBT of Example 5 above in the same manner as in FIG. 15 (normalizingmelting energy and plotting against chain extender content).

Example 7

As base polymer, a polyamide 12 (PA12) material was used. The polyamide12 used was Vestamid LX 9012 (obtainable from Evonik Industries AG,Marl). As blowing agent, a combination of 4% by weight of(supercritical) carbon dioxide and 3% by weight of ethanol, based on100% by weight of the base polymer, was used. A chain extender based onstyrene-acrylate copolymer, namely Joncryl® ADR-4368C (BASF), was usedin the amount of 1.5% by weight, based on 100% by weight of the basepolymer, and without chain extender.

The polymer together with the same blowing agent and the indicatedamount of chain extender were melted in an extruder, similar toExample 1. Subsequently, similar to Example 1 the melt was expandedthrough a round die and fed to an underwater pelletizing device toobtain expanded pellets.

In FIGS. 16 and 17, scanning electron microscopy (SEM) images of theexpanded polyamide pellets are shown. FIG. 16 shows the pellets without(0%) chain extender, FIG. 17 with 1.5% chain extender. The enlargementscale in those figures is 200-times of a distance of 100 μm as shown.The images show that the pellets have partially ruptured foam structure,shown by the ruptures in the cell walls which increases with the amountof chain extender, thus providing an excellent foam structure for soundinsulation.

1. Method for producing expanded polymer pellets, comprising thefollowing steps: a. melting a polymer comprising a polyamide; b. addingat least one blowing agent; c. expanding the melt through at least onedie for producing an expanded polymer; and d. pelletizing the expandedpolymer.